CO2浓度升高条件下小麦根系吸水特性的变化及其定量表征

In addition to water shortage, agricultural production in China has to deal with the influence resulted from the gradually elevated atmospheric CO2 concentration. As an important substrate for photosynthesis, the change of CO2 concentration will have a number of effects on root-water-uptake. Under conditions with higher CO2 concentration, the water absorption function of roots and root growth might be limited or promoted somehow, and the effects on both of them might get smaller and even disappear with the extension of adaptation time. However, the effects were not and could not be taken into consideration by the existing root-water-uptake models and root-growth-distribution models. In this study, the effects of elevated CO2 on water absorption function of roots (the potential root-water-uptake coefficient per unit root nitrogen mass) and on root growth and distribution (the root nitrogen allocation factor and the root nitrogen mass density profile) will be investigated and quantitatively described. To achieve this objective, a solution cultivation experiment and a soil column experiment in a greenhouse will be conducted for wheat, as well as a field experiment. Subsequently, the existing root-water-uptake models and root-growth-distribution models based on root nitrogen mass density will be improved, and the dynamics regarding root growth and distribution, water uptake, and soil water transport will be simulated. The findings will not only enhance the theoretical system regarding root growth and water uptake, but also will become the scientific evidence and technical storage to efficiently use agricultural water resources under elevated CO2 in the future.

除水资源短缺外，我国农业生产还将不得不面临大气CO2浓度逐年升高所带来的影响。CO2是作物进行光合作用的物质基础，其浓度的变化势必会对根系吸水产生较大影响。在CO2浓度升高条件下，根系吸水性能和根系生长都可能会受到不同程度的抑制或刺激，且这些影响都可能随作物适应时间的延长而降低甚至丧失。然而，现有根系吸水模型与根系生长分布模型都没有、也无法对其予以考虑。以大气CO2浓度升高为背景，通过布置小麦室内水培试验、土柱试验以及田间试验，本项研究拟探索并定量表征小麦根系吸水性能（单位质量根氮潜在吸水系数）与根系生长分布（根氮分配与根氮质量密度分布）所受到的影响，从而对已有基于根氮质量密度的根系吸水模型以及根系生长分布模型予以改进，并对根系生长分布、根系吸水以及土壤水分运移进行动态模拟。相关研究成果不仅可完善根系吸水与生长相关理论，还可为CO2浓度升高条件下农业水资源的高效利用提供科学依据与技术储备。

除水资源短缺外，我国农业生产还将面临大气CO2浓度逐年升高带来的影响。CO2是作物光合作用的物质基础，其浓度变化势必会对地上部与根系生长以及根系吸收产生影响，并且影响程度还会随适应时间的延长而发生改变。然而，现有根系吸水模型与生长分布模型都没有、也无法对其予以考虑。以大气CO2浓度升高为背景，通过布置2个小麦室内水培试验与1个室内砂培试验，本项研究探索并定量表征了小麦根系吸水性能与根系生长分布所受到的影响，从而对已有根系吸水模型以及生长分布模型予以改进，并对高CO2浓度条件下作物缺氮原因开展了研究。结果表明：（1）短期内，CO2浓度升高导致小麦叶片气孔导度迅速降低，光合作用增强，蒸腾耗水与根系吸水降低，根系吸水性能减弱，水分利用效率升高；（2）随着被置于高CO2浓度条件下时间的延长，叶片水汽交换所受影响程度逐渐缩小，即发生了CO2驯化现象，但此时小麦地上部与根系生长更为旺盛，蒸腾耗水与根系吸水并未发生显著变化，根系吸水性能降低，水分利用效率升高；（3）CO2浓度升高导致小麦总吸氮量增加，但不会对根氮浓度造成显著影响，仅在低氮供应条件下才会显著降低地上部氮浓度，此时更多氮素被分配于根系中；（4）小麦通过改变根系吸氮方式（根系吸氮因子）来适应外界环境条件（大气CO2浓度与土壤供氮能力）的变化从而满足自身对氮素的需求，因此高CO2浓度条件下作物缺氮并不是由根系吸水或蒸腾降低所致，也不是由植物体内NO3-同化受限所致，而是由光合产物积累速度过快所致，即稀释效应；（5）CO2浓度升高有助于根系生长，尤其表层土壤中的根长密度与根氮质量密度都显著增大，但这几乎不会改变根系的相对分布规律，仍可以用统一幂函数予以定量描述。以上相关研究成果不仅可完善根系吸水与生长相关理论，还可为CO2浓度升高条件下作物生长模拟以及农业水资源高效利用提供科学依据与技术储备。